package com.hqd.ch03.v46.boot.context.properties.source;

import com.hqd.ch03.v46.core.env.*;

import java.util.Collections;
import java.util.stream.Stream;

public final class ConfigurationPropertySources {

    /**
     * The name of the {@link PropertySource} {@link #attach(Environment) adapter}.
     */
    private static final String ATTACHED_PROPERTY_SOURCE_NAME = "configurationProperties";

    private ConfigurationPropertySources() {
    }

    /**
     * Create a new {@link PropertyResolver} that resolves property values against an
     * underlying set of {@link PropertySources}. Provides an
     * {@link ConfigurationPropertySource} aware and optimized alternative to
     * {@link PropertySourcesPropertyResolver}.
     *
     * @param propertySources the set of {@link PropertySource} objects to use
     * @return a {@link ConfigurablePropertyResolver} implementation
     * @since 2.5.0
     */
    public static ConfigurablePropertyResolver createPropertyResolver(MutablePropertySources propertySources) {
        return new ConfigurationPropertySourcesPropertyResolver(propertySources);
    }

    /**
     * Determines if the specific {@link PropertySource} is the
     * {@link ConfigurationPropertySource} that was {@link #attach(Environment) attached}
     * to the {@link Environment}.
     *
     * @param propertySource the property source to test
     * @return {@code true} if this is the attached {@link ConfigurationPropertySource}
     */
    public static boolean isAttachedConfigurationPropertySource(PropertySource<?> propertySource) {
        return ATTACHED_PROPERTY_SOURCE_NAME.equals(propertySource.getName());
    }

    /**
     * Attach a {@link ConfigurationPropertySource} support to the specified
     * {@link Environment}. Adapts each {@link PropertySource} managed by the environment
     * to a {@link ConfigurationPropertySource} and allows classic
     * {@link PropertySourcesPropertyResolver} calls to resolve using
     * {@link ConfigurationPropertyName configuration property names}.
     * <p>
     * The attached resolver will dynamically track any additions or removals from the
     * underlying {@link Environment} property sources.
     *
     * @param environment the source environment (must be an instance of
     *                    {@link ConfigurableEnvironment})
     * @see #get(Environment)
     */
    public static void attach(Environment environment) {
        MutablePropertySources sources = ((ConfigurableEnvironment) environment).getPropertySources();
        PropertySource<?> attached = getAttached(sources);
        if (attached == null || !isUsingSources(attached, sources)) {
            attached = new ConfigurationPropertySourcesPropertySource(ATTACHED_PROPERTY_SOURCE_NAME,
                    new SpringConfigurationPropertySources(sources));
        }
        sources.remove(ATTACHED_PROPERTY_SOURCE_NAME);
        sources.addFirst(attached);
    }

    private static boolean isUsingSources(PropertySource<?> attached, MutablePropertySources sources) {
        return attached instanceof ConfigurationPropertySourcesPropertySource
                && ((SpringConfigurationPropertySources) attached.getSource()).isUsingSources(sources);
    }

    static PropertySource<?> getAttached(MutablePropertySources sources) {
        return (sources != null) ? sources.get(ATTACHED_PROPERTY_SOURCE_NAME) : null;
    }

    /**
     * Return a set of {@link ConfigurationPropertySource} instances that have previously
     * been {@link #attach(Environment) attached} to the {@link Environment}.
     *
     * @param environment the source environment (must be an instance of
     *                    {@link ConfigurableEnvironment})
     * @return an iterable set of configuration property sources
     * @throws IllegalStateException if not configuration property sources have been
     *                               attached
     */
    public static Iterable<ConfigurationPropertySource> get(Environment environment) {
        MutablePropertySources sources = ((ConfigurableEnvironment) environment).getPropertySources();
        ConfigurationPropertySourcesPropertySource attached = (ConfigurationPropertySourcesPropertySource) sources
                .get(ATTACHED_PROPERTY_SOURCE_NAME);
        if (attached == null) {
            return from(sources);
        }
        return attached.getSource();
    }

    /**
     * Return {@link Iterable} containing a single new {@link ConfigurationPropertySource}
     * adapted from the given Spring {@link PropertySource}.
     *
     * @param source the Spring property source to adapt
     * @return an {@link Iterable} containing a single newly adapted
     * {@link SpringConfigurationPropertySource}
     */
    public static Iterable<ConfigurationPropertySource> from(PropertySource<?> source) {
        return Collections.singleton(ConfigurationPropertySource.from(source));
    }

    public static Iterable<ConfigurationPropertySource> from(Iterable<PropertySource<?>> sources) {
        return new SpringConfigurationPropertySources(sources);
    }

    private static Stream<PropertySource<?>> streamPropertySources(PropertySources sources) {
        return sources.stream().flatMap(ConfigurationPropertySources::flatten)
                .filter(ConfigurationPropertySources::isIncluded);
    }

    private static Stream<PropertySource<?>> flatten(PropertySource<?> source) {
        if (source.getSource() instanceof ConfigurableEnvironment) {
            return streamPropertySources(((ConfigurableEnvironment) source.getSource()).getPropertySources());
        }
        return Stream.of(source);
    }

    private static boolean isIncluded(PropertySource<?> source) {
        return !(source instanceof PropertySource.StubPropertySource)
                && !(source instanceof ConfigurationPropertySourcesPropertySource);
    }

}
